Hi all,
Darrel do you know the numbers on this statement? Just curious what the values are.
I'll have a go at these.
The original paper on the complete oxidation of ammonia to nitrate by
Nitrospira spp. (complete ammonia oxidation; comammox) is Van Kessel
et al. (2015) <"
Complete nitrification by a single microorganism">
Nature. 2015 Dec 24; 528(7583): 555–559.
The bacteria were identified in a bio-filter from Common Carp (
Cyprinus carpio) RAS aquaculture, and this contained 0 - 75 µM NH4+. The RMM of NH4 is 18 (14+4), so a 0.75M solution of NH4+ would contain 18*0.75 = 13.5g NH4+ in 1 litre of water.
Then we just need to do some sorting out with "powers of 10". A "µM" is 10-6 Mol, so we use 13.5/1,000,000 (1*10^6) = 0.0000135 to give us a weight of NH4+ in grams.
Then ppm is equivalent to mg/l, so we multiply 0.0000135*1000 (1*10^3) to give us 0.0135 ppm NH4+ (or we can take the two ^10 away from one another and divide 13.5/1000). In the paper they used a top ammonium loading of 500 µM NH4+ which (0.0135 * 6.667) gives 0.9 ppm NH4+. The reactor was maintained at pH7.
There is probably a more modern reference, but the top level of NH4+ used may relate to the work of Kim, Lee & Keller (2006) <"
Effect of temperature and free ammonia on nitrification and nitrite accumulation in landfill leachate and analysis of its nitrifying bacterial community...">
Bioresour Technol. 2006 Feb;97(3):459-68.
......The activity of NOB was inhibited by NH3-N resulting in accumulation of nitrite. NOB activity decreased more than 50% at 0.7 mg NH3-N L(-1)....
Tens of ppms of ammonia.... and the nitrifying population is apparently a lot more sensitive to pH than to ammonia levels, irreversibly so. They adapt to different ammonia levels. The levels that drastically change the populations are way higher than the ones in aquariums, even the ones used in fishless cycle.
All the work I've read would strongly suggest that even small increases in ammonia loading drastically effect the microbial community. The initial reference would be Bartelme
et al. (2017) <"
Freshwater Recirculating Aquaculture System Operations Drive Biofilter Bacterial Community Shifts around a Stable Nitrifying Consortium of Ammonia-Oxidizing Archaea and Comammox Nitrospira">
Front Microbiol. 2017; 8: 101. This had a top level of about 14 µM NH3
.......RAS operations data was examined from the beginning of a Yellow perch rearing cycle until ~6 months afterward. The mean biofilter influent concentrations of ammonia and nitrite were, respectively, 9.02 ± 4.76 and 1.69 ± 1.46 μM. Biofilter effluent ammonia concentrations (3.84 ± 7.32 μM) remained within the toxicological constraints (<60 μM) of P. flavescens reared in the system.
However, in the context of the planted tank, and assuming that the time scale for the development of the microfauna is so short, why do we usually assume the tank is cycled not before a month or so? Also, in this respect, what is the definition of matured tank, and why do we usually expect that to happen only a few months after start?
Because we (newbies and non-specialist) associate the concept "cycled" to the Nitrogen - cycle and this to bacteria communities... And what is "Matured" tank in this context? Why does it take so long?
It is like Clive
@ceg4048 says the microbial community will always change dependent upon oxygen, ammonia, carbon etc. availability. If you just ignore the filter for a minute, and think about the substrate, as roots grow (and senesce) they will create gradients of carbon, oxygen and nutrient availability. As a general rule in ecology complexity brings stability and resilience, and species diversity (but not biomass) is highest in patchy, low nutrient situations. Since we had the ability to look at microbial DNA we've found thousands of "new" micro-organisms in bio-filters. From the Bartelme
et al. paper ....
...We found the biofilter community harbored a diverse array of bacterial taxa (>1000 genus-level taxon assignments) dominated by Chitinophagaceae (~12%) and Acidobacteria (~9%). The bacterial community exhibited significant composition shifts with changes in biofilter depth and in conjunction with operational changes across a fish rearing cycle. Archaea also were abundant, and were comprised solely of a low diversity assemblage of Thaumarchaeota (>95%), thought to be ammonia-oxidizing archaea (AOA) from the presence of AOA ammonia monooxygenase genes.
You can create a low diversity microbial environment by having high ammonia loadings and a bare tank (no plants or substrate), and the biofilter will develop the bacterial community that we were told we needed to "cycle" our tanks. It is a black and white scenario, bacteria present = cycled, but it doesn't have to be like that and I'm personally convinced that it isn't the best option for 99% of fish keepers.
cheers Darrel